Excessive noise when in lowest gear

[T4tomo]

Before forking out any cash (or bank details) for a new mech, just try a different mech (OP (still) gives no idea of the bike/RD/speed).
I'd also actually check the hanger's verticality.
As for "the spring on the rear mech is not quite doing enough to sit precisely in the right position when on the largest sprocket" Yeah: right. The lateral position of the guide pulley is determined by, inter alia, the cable pull and shift ratio (and the L limit screw will position the RD over the large sprocket). The spring makes sure the cage moves down the cassette and has minimal function when on the large sprocket.

agree, bolded statement is bollox.

@Fifelad if the hanger is slightly out, you will be able to tune out the noise using the alignment adjust / indexing (which will put the indexing out on the smaller sprockets)

if you cant "index" the noise away, then its something else

 

[Fifelad]

Don't stop there - get his bank details

Road bike, 11-32 ratio, double chain ring 50-34 at the front. Shimano Ultegra 6800.

 

[Ajax Bay]

Road bike, 11-32 ratio, double chain ring 50-34 at the front. Shimano Ultegra 6800.

Thank you, and to @Cycleops for asking. I shall guess this is an RD-6800-SS. If so, OP is asking it to perform out of spec on two counts: capacity (33) and largest sprocket (28t). Is it surprising the largest sprocket is a challenge? [Cue shedloads of chatters saying they've managed it no prob.]
If it's a GS then set up is within spec. Check hanger.
https://bike.shimano.com/en-EU/product/component/ultegra-6800/RD-6800-SS.html

Total capacity	33T
Low sprocket|Max.	28T

 

[Ajax Bay]

Just fitted new rear derailleur cables inner and outers, jockey wheels still in good conditon and the gears are indexing perfectly, it’s just when in the lowest gear there is excessive noise like the chain is not sitting exactly right on the jockey wheels.

I thought you'd had something like this before (so stalked):
https://www.cyclechat.net/threads/gear-indexing-perfectly-except-for-the-lowest-gear.269868/
What did you learn the last time? (2020!)

I have recently replaced my rear gear cable, and the indexing is perfect, except that the lowest gear even though the chain shifts on to the biggest cog no bother, there is a noise where the chain appears to be not sitting dead right on the jockey wheels. Any ideas ?

 

[Fifelad]

So, to clarify, a new mech fitted has solved the issue. My previous statement regarding the issue of the derailleur spring was my error, I had misinterpreted what had been said by the LBS mechanic, he was of the opinion that the mech was “tired” and it was difficult to pin point exactly what the issue with it was, be it pivots, etc. He also checked if the existing rear mech was within the capabilities of the gear ratios and it was. Before he commenced the work he told me that if it didn’t work, I would obviously not be charged for the mech, which was sourced at a considerable reduced price, and he did try to find an older one to to try first but had none to hand. I can’t help thinking that my previous issue was as a result of this too, ie the start of the mech not being as efficient as it should of been, but previously rectified by B screw adjustment in the past. I hope this explanation fully clarifies everything and fully exonerates me from further interrogation, particularly from Ajax. 🤷‍♂️😂

 

[Ajax Bay]

Do 'they' put specially weak springs in 11sp RDs which (for reason unknown) suffer (unplanned?) deterioration. How can a spring get "tired"? (when operated within its limits as in an RD)
And why would that affect accurate guidance of the chain onto the largest sprocket?
The cage is pulled up there (and held) by the cable.
Glad you have it sorted, @Fifelad nevertheless.